The present invention relates to shock absorbers and more particularly a shock absorber that utilizes different fluids for isolating or cushioning the ride of a vehicle to which the shock absorber is coupled.
A suspension system for a vehicle typically includes the use of shock absorbers, shock absorbing struts and/or suspension springs to provide a cushioned ride for the driver and the passengers, if any, of the vehicle. A conventional shock absorber has a chamber filled with hydraulic oil in which a piston connected to a piston rod is moved. The viscosity of the oil in the cylinder provides damping for the movement of the piston rod relative to the cylinder so that any vibration or bump to either the cylinder or the piston rod that result from sudden jolts to the vehicle is modulated.
A second type of shock absorber consists of gas shocks that utilize pressurized gases for damping the movement of the piston rod. Yet a third type of suspension system comprises a combination of both oil and gas. For this type of suspension system, there is provided an external reservoir for the oil that is separate from the shock absorber cylinder. In this reservoir, there is stored, in addition to the oil, a pressurized gas that provides a biasing force against the oil so that, when oil is needed in the cylinder, the oil in the reservoir is forced by the pressurized gas to fill up the cylinder. When under pressure in the cylinder, the excess oil is forced out of the cylinder and stored in the reservoir.
Such external oil reservoir suspension system is taught for example in U.S. Pat. Nos. 4,593,921 and 5,486,018. These systems work well. However, due to its bulkiness, such system requires a large amount of space which may not be available for certain types of vehicles such as for example snowmobiles. Moreover, due to the need for the extra reservoir and the conduits necessary for connecting the reservoir to the shock absorber, the cost for such system is much higher and therefore could not be justified in most types of vehicles. Furthermore, due to the extra valves and controls that are required to regulate the flow of fluid between the shock absorber and the reservoir, not only is the cost high, the maintenance for such system likewise is greater than that required for a typical suspension system. Lastly, the chances of a breakdown for such suspension system are increased due to the additional components required.
The present invention shock absorber uses a combination of different types of fluids for effecting damping. In particular, the present invention shock absorber looks like a conventional shock absorber from the outside but is constructed to have an inner chamber and an outer chamber in concentric relationship with the inner chamber. For example, the outer chamber is constructed to surround at least a portion of the inner chamber. The inner chamber is filled with an incompressible fluid such as for example a hydraulic oil. A number of orifices are provided between the inner chamber and the outer chamber so as to enable fluid communication between the inner and outer chambers. A piston rod extends through an opening at one end of the inner chamber and is coupled or bolted to a piston that fits within the inner chamber in a fluid tight manner so as to separate the inner chamber into two portions. At the portion of the inner chamber where the orifices are located there is provided the incompressible fluid such as for example the hydraulic oil.
Concentrically fitted about the inner chamber is a moveable piston that provides a fluid tight seal within the outer chamber. This piston seal in the outer chamber, like its inner chamber counterpart, also separates the outer chamber into two portions or compartments. The compartment that is in fluid communication with the inner chamber by means of the orifices is likewise filled with hydraulic oil, while the compartment separated from the oil filled compartment is filled with a pressurized gaseous fluid.
By adjusting the pressure of the gas provided in the gas compartment of the outer chamber, a desired stiffness could be obtained for the shock absorber. To further define the stiffness of the shock absorber, the flow rate of the oil between the inner chamber and the outer chamber can be regulated by adjusting the size of the orifices that provide the fluid communicative passage between the inner chamber and the outer chamber. Such adjustment may be made by fitting to at least one of the orifices a conventional needle valve. Thus, the movement of the piston rod relative to the shock absorber cylinder is damped by the hydraulic oil in the inner chamber, the flow rate by which the oil is exchanged between the inner and outer chambers, and the pressurized gas that provides the bias force against the hydraulic oil.
The shock absorber of the present invention is further provided with an air cushion assembly in the form of an elastomeric boot that sealingly covers the portion of the piston rod that extends from the cylinder body. When the elastomeric boot, or bag, is pressurized with the appropriate amount of gaseous fluid such as for example air, an additional damping attribute is provided. To prevent the mounting bracket to which the piston rod is connected from collapsing into the shock absorber cylinder, a spring is fitted about the piston rod between the mounting bracket and the body of the cylinder. An additional spring may be provided about the portion of the piston rod within the inner chamber so as to prevent the rod from collapsing against the opening when the portion of the piston rod within the inner chamber is moved towards the opening.
A second embodiment of the shock absorber of the instant invention has the outer chamber thereof partitioned by a pair of moveable pistons into three separate compartments. The portions of the inner chamber that are separated by the piston connected to the piston rod in turn each have a number of orifices for forming fluid communication passages with their corresponding end compartments of the outer chamber. Thus, as the piston rod is moved by the bumps that the vehicle which the shock absorber is coupled to encounters, the oil in the inner chamber is exchanged with both end compartments of the outer chamber, with one of those end chambers storing the oil forced out of the inner chamber while the other end compartment outputting oil to the inner chamber, to thereby provide a balancing but yet damping influence on the vehicle.
Another embodiment of the shock absorber of the instant invention utilizes particular cavities or bores that coact with plunger mechanisms for providing additional damping attributes to the shock absorber. In particular, a cavity and a bore could be strategically formed in the inner chamber of the housing, and also in the mounting bracket of the shock absorber assembly. Corresponding puncher mechanisms are integrated to the piston of the piston rod and also to the housing so that when the plunger mechanism at the piston coacts or mates with the cavity formed inside the inner chamber, a damping resistance force is built up to act against the movement of the piston, thereby. damping the movement of the piston rod relative to the housing of the shock absorber. Such resistance force adds damping to the shock absorber in the event that the piston rod is being pulled away from the housing of the shock absorber.
In the event that the piston rod and the housing are being pushed toward each other, the bore formed at the mounting bracket will coact with a plunger mechanism formed at the housing so as to generate a resistance force when the plunger mechanism at the housing mates with the bore at the mounting bracket. Again, a resistance force is generated to provide damping for the shock absorber assembly, in this instance when the shock absorber assembly is being compressed.
It is therefore an objective of the present invention to provide a shock absorber that is highly effective in that it uses a number of interacting fluids for defining its stiffness.
It is another objective of the present invention to provide a shock absorber that has an outside appearance that looks substantially like a conventional shock absorber and yet contains therewithin an oil reservoir that prior art shock absorbers do not have.
It is yet a further objective of the present invention to provide a shock absorber that has the damping attributes of a combination air and oil shock isolation system but yet at the same time is structurally small enough to fit into small vehicles such as for example snowmobiles.